Column flotation cell for enhanced recovery of minerals such as phosphates by froth flotation

ABSTRACT

An apparatus for separating a mineral from a slurry of mineral and impurities, including a fluid vessel having a first, open end and a second end and a feed well disposed near the first end. The feed well has a first, open end, for receiving the slurry, and a second end. At least one first member is received through the first ends of the vessel and the feed well for providing aerated water, creating a froth in the feed well including substantially the mineral. The mineral froth substantially separates from the impurities and floats out of the feed well towards the first end of the vessel, and a collection unit receives the mineral froth. The impurities and any remaining mineral fall toward the second end of the vessel. A measurement unit is placed within the vessel for measuring at least one of density and pressure of the fluid in the vessel. A related process includes introducing the slurry into the first, open end of the feed well, providing aerated water to the feed well and the vessel in a direction from the first ends to the second ends, respectively, creating a froth in the feed well including substantially the mineral, substantially separating the mineral froth from the impurities, collecting the mineral froth, and allowing the impurities and any un-separated mineral to fall towards the second end of the vessel. Further, the process includes measuring at least one of density and pressure of the fluid in the vessel.

RELATED APPLICATION

This application is a division of application Ser. No. 11/099,940 filedApr. 6, 2005, which claims the benefit of U.S. Provisional ApplicationNo. 60/582,862 filed Jun. 28, 2004 and U.S. Provisional Application No.60/583,606 filed Jun. 30, 2004, each of which is hereby fullyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to the recovery of minerals such asphosphate and, more particularly, to a column flotation cell and relatedmethod to enhance phosphate recovery.

2. Description of Related Art

Presently, phosphate is recovered from a sand-clay mixture that is minedfrom mineral deposits. Traditionally, phosphate is mixed with acollector, suspended in water and urged to the surface of an aerationtank called a flotation cell.

For example, as shown in FIG. 1 herein, U.S. Pat. No. 4,735,709describes a flotation system 10 with means for introducing a gaseousmedium such as air, to facilitate flotation. The system 10 generallyincludes a flotation vessel 12, and two air sparger systems 14 and 16for introducing a gaseous medium or air into the vessel 12.

The vessel 12 is formed as an upright elongated cylinder having avertical wall 18 and a bottom wall 20. The vessel 12 is typically openat an upper end 22. A substantially horizontally-disposed constrictionplate 24 is located within the vessel 12, spaced above the bottom wall20, to separate the vessel 12 into a flotation compartment 26 above theconstriction plate 24 and a distribution compartment 28 below theconstriction plate 24. The constriction plate 24 has a plurality oforifices 30 to permit passage of aerated water from the distributioncompartment 28 to the flotation compartment 26.

A feed well 32 is supported within the upper end 22 of the flotationcompartment 26 by a base 33. A feed tube 34 from an external source ofaqueous slurry (not shown) delivers a controlled quantity of the aqueousslurry to the feed well 32. The feed well 32 has an overflow baffle 36to distribute the aqueous slurry throughout the flotation compartment26. The feed well of this conventional design is located under the waterlevel 11 in the vessel 12.

Air bubbles are introduced into the bottom of the fluid vessel 12 byflowing aerated water through the air sparger 14 and into a manifold 38exiting into the vessel 12 via the orifices 30. The air bubbles aeratethe slurry in the vessel 12.

The slurry entering vessel 12 contains phosphate, impurities and acollector. The use and types of collectors are well known in the art. Anexample of a typical collector used in the art is a hydrocarbon such astall oil. See, e.g., U.S. Pat. No. 6,178,383. The phosphate suspended inthe aqueous slurry adheres to the rising air bubbles and collects at theupper end of the flotation compartment 26 as a froth.

A launder 44 is provided at the upper end 22 of the vessel 12, atop thecylinder wall 18. The launder 44 generally includes a circular innerwall 45, a relatively higher outer wall 47 and a bottom wall 49 thatform a trough 51 to receive the froth, which overflows from theflotation compartment 26. The froth overflows into the trough 51 whenthe froth inside the flotation compartment 26 rises and spills over thetop of the lower circular inner wall 45. An outlet 46 is provided in theouter wall 47, near the bottom wall 49, to convey the overflowingphosphate-laden froth from the launder 44 to further processing orstorage.

The impurities including sand and clay contained within the slurry alongwith any residual phosphate that is not captured by the levitating airbubbles percolates downwardly through the aqueous slurry by gravity. Anopening 48 is formed through the center of the constriction plate 24into which the impurities pass through. An outlet 50 extends from theopening 48 through the bottom wall 20 of the cylinder 12. The outlet 50allows removal of the impurities from the vessel 12.

The orifices 30 can “choke” over a period of time because the velocityof the air bubbles moving through the orifices 30 is not high enough toprevent the downwardly percolating impurities including sand fromplugging the orifices 30. The result of the choking is that aeratedwater will not be able to enter and circulate through the vessel 12,which results in poor separation of the phosphate from the impurities.

Further, the system 10 generally exists an as alkaline environment,which can allow algae growth. Algae growth is promoted near the orifices30 because the levitating air bubbles create low-turbulence areas nearthe orifices 30. Algae will attach and grow at these low-turbulenceareas such that over time the orifices 30 will get sealed off,preventing the even dispersion of aerated water throughout the vessel12.

U.S. Pat. No. 4,735,709 also describes the use of a separate air spargersystem 16 that discharges aerated water above the constriction plate 24into the vessel 12 via orifices 41 in pipes 40. However, these orifices41 can also choke over a period of time as the impurities from theslurry percolate downward in the vessel 12 for the same reasons asdescribed above.

The choking of the orifices 30 and 41 can not only prevent the evenaeration of the vessel 12, but also require maintenance involving thecleaning or redrilling of the orifices 30 and 41 in order to un-choke orun-plug them. The phosphate separation process, therefore, has to besuspended for maintenance and cannot be carried on as a continuousprocess. A continual need for maintenance introduces down time andmaintenance costs into the separation process, which results in reducedrecovery of phosphate and high cost of operation.

As also known in the art, the above-described column flotation cell canrequire significant capital expenditures to build, depending upon thesize, component parts, etc. The system is also known to require asignificant amount of energy to thrust aerated water from the bottom tothe top of the column flotation cell.

Thus, although the prior art described above has generally been widelyused for the purposes of recovering minerals such as phosphate fromimpurities, it still does not disclose or teach a column flotation celland a method of use that reduces capital costs, lowers energyconsumption, prevents substantial choking of the column and allowseasier maintenance.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide anapparatus and process for separating minerals such as phosphate fromimpurities using a column flotation cell that substantially eliminateschoking.

It is another aspect of the present invention to provide an apparatusand process for recovering phosphate using a column flotation cell thatis easier to maintain.

It is another aspect of the present invention to provide an apparatusand process for recovering phosphate using a column flotation cell thatutilizes a cell density control process wherein the density within thecolumn is monitored to regulate the discharge of impurities from thebottom of the column influenced by the amount of incoming slurry.

It is also an aspect of the present invention to provide an apparatusand process for recovering phosphate using a column flotation cellreceiving aerated water via down pipes to substantially eliminatechoking and improve dispersion of air into the cell.

It is a further aspect of the present invention to provide an apparatusand process for enhanced recovery of phosphate that uses less energy peryield.

Finally, it is an aspect of the present invention to provide anapparatus for recovering phosphate having a substantially compact designto reduce capital cost for installation and maintenance.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a perspective, partial cross-sectional view of a prior artcolumn floatation cell.

FIG. 2 is a schematic view of a separation system according to anembodiment of the present invention, including a pair of interconnectedcolumn floatation cells.

FIG. 3 is a side, elevational view of a column used with the columnflotation cell of the present invention.

FIG. 4 is a left side, elevational view of a launder used with thecolumn flotation cell of the present invention.

FIG. 5 is a front, elevational view of the launder shown in FIG. 4.

FIG. 6 is a side, elevational view of one column flotation cellaccording to an embodiment of the present invention.

FIG. 7 is a top plan view of a column flotation cell according to anembodiment of the present invention.

FIG. 8 is a side cross-sectional view of a feed well according to anembodiment of the present invention.

FIG. 9 is a schematic view of the cell density control process accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments of the present invention will now be described withreference to the drawings. In this description, certain dimensions areused to assist in understanding the structure of the invention. Ofcourse, one of ordinary skill in the art may vary the dimensions withoutdeparting from the invention. As a result, it is not intended that theinvention be limited by any particular dimensions.

FIG. 2 is a schematic view of a separation system 60 according to anembodiment of the present invention. The system 60 includes generally apair of interconnected column floatation cells, i.e., a primary cell 62and a secondary cell 64, each having similar constructions, as describedbelow.

The two cells 62 and 64 are placed at different heights and areinterconnected for a staged separation of a feed slurry havingphosphate, impurities such as sand and clay, and one or more knowncollectors such as tall oil. The incoming feed slurry is referred toherein as “A”.

Although in this embodiment two cells are described and shown, othernumbers of cells, including one, may be used. Use of multiple stagedcells achieves a higher phosphate recovery from A.

Into the primary cell 62 there extends a feed tube 66 extending from aconventional slurry source 68. An outlet 108 is formed at a bottom 102,described below, of the primary cell 62 and is connected to a pipe 72,which leads to another feed tube 74.

A water line 70 having a pair of eductors 92 supplies aerated water andone or more known frothers such as polyglycol into the cells 62 and 64,respectively. Eductors 92 are aspirators that introduce air into thewater coming through the water line 70. Valves 96 control the amount ofwater passing to the eductors 92. Air is introduced into the waterentering the eductors 92 via valves 98 to generate aerated water.Therefore, both the amount of water and air passing through the eductors92 are adjustable.

Down pipes 90 are connected to the eductors 92 and thrust the aeratedwater into the primary and secondary cells 62 and 64. The down pipes 90are preferably clamped to a baffle 160 located near the top of eachcell, as described below, and terminate near the bottom 102 of bothcells 62 and 64 (see FIG. 6). Down pipes 90 are also preferably clampedto sides 144 of feed wells 140 in each of the cells 62 and 64. The downpipes 90 terminate near the bottom 142 of the feed wells 140 within bothcells 62 and 64 (see FIG. 8).

The feed slurry A entering cell 62 via feed tube 66 pours into the feedwell 140, where the separation process begins. Phosphate froth isgenerated due to the air bubbles rising in the feed well 140 asdescribed below. In the first step of separation, the feed well 140separates much of the impurities contained in A from the phosphate tocreate phosphate froth substantially free from impurities. Thisphosphate froth is referred to herein as “C” and the separatedimpurities are referred to herein as “B”.

C is thrust upward out of the feed well 140 and into a column 100 ofcell 62 as the phosphate froth rises towards a top 146 of the feed well140 continuing to a top 106 of the column 100 (see FIGS. 6 and 8). Therise of the phosphate froth C is promoted by the thrust of the risingair bubbles and the hydrophobicity of the collector in the phosphatefroth C. The hydrophobicity of the phosphate froth C renders it amenableto flotation by attachment to the rising air bubbles. The impurities Balong with any un-separated phosphate fall toward the bottom 102 of thecolumn 100. The separation process is completed in the column 100 whererising air bubbles from the bottom 102 of the column 100 generate anupward thrust of air, referred to herein as “air hold-up”. C then spillsout of the top 106 of the column 100 into the launder 120 as the top 106of the column 100 is lower than a top 124 of the launder 120. (Seediscussion below regarding FIG. 6).

The launder 120 of the primary, upper cell 62 has an outlet 128, whichdraws off the separated phosphate froth C and sends it via an outflowpipe 80 for further processing or storage, as in the prior art describedabove.

The impurities B and the remaining un-separated phosphates at the bottom102 of the column 100, exit cell 62 via the outlet 108. A pinch valve 94controls movement of the impurities B and the remaining un-separatedphosphates through the outlet 108. The column 100 of the secondary,lower cell 64 also has an outlet 108 controlled by a pinch valve 94. Thefeed tube 74 introduces the impurities B and the remaining un-separatedphosphates, herein referred to as A′, into the feed well 140 of thesecondary cell 64 for staged separation. Therefore, A′ collected fromcell 62 is separated again in cell 64 allowing for improved recovery ofphosphate.

The outlet 128 of the launder 120 of the lower, secondary cell 64 allowsremoval of the separated phosphate froth C via an outflow pipe 82 in amanner similar to that described above for further processing orstorage. The outlet 108 on the secondary cell 64 allows the impurities Bsuch as sand and clay particles that accumulate along with anyunrecovered phosphate near the bottom 102 of the column 100 to be drawnoff via a pipe 79. These impurities B and any unrecovered phosphate caneither be disposed of or directed to another staged cell for furtherprocessing in order to recover additional phosphate.

FIG. 3 illustrates in greater detail the column 100 of the columnflotation cells 62 and 64. A central axis is shown by “Y”. The column100 includes the solid bottom 102 and a substantially columnar sidewall104, which is open at the top 106. The diameter of the sidewall 104increases from the bottom 102 to the top 106 of the column 100. Due tothe differences in diameter, there are formed a lower columnar portion110, a middle beveled portion 112, and an upper columnar portion 114.The bottom 102 includes the outlet 108, which allows the removal of A′from the bottom 102 of the column 100 in cell 62.

In a preferred embodiment of the present invention, the height of thecolumn 100 is about 6 feet. The external diameter at the top 106 of thecolumn 100 is preferably about 10 feet. Both the external diametertowards the top of the column and the height of the column 100 may be inthe range of about 3-40 feet. The ratio of the external diameter of thetop 106 of the column 100 to the height of the column 100 is in therange of about 0.5-2.0. More preferably the ratio is in the range ofabout 0.6-1.33. Therefore, unlike conventional columns that have aheight that is much greater than the width, the present invention canuse the reverse configuration, i.e., a height that is less than thediameter of the column. This configuration allows the system 60 of thepresent invention to be more compact, requiring less energy to thrustwater from the bottom 102 of the column 100 via down pipes 90.

FIG. 4 is a left side elevational view, and FIG. 5 is a frontelevational view, of the launder 120 used with the cells 62 and 64. Thelaunder 120, like the column 100, is generally cylindrical, having abottom 122, a top 124 and a sidewall 126. The bottom 122 is angledrelative to the top 124.

The diameter of the sidewall 126 increases from the bottom 122 to thetop 124 of the launder 120. Due to this difference in diameter, there isformed a lower angled portion 132, a middle beveled portion 134, and anupper columnar portion 136. A trough 138 (FIGS. 6 and 7) is formedbetween the upper portions of the column 100 and launder 120 forcollecting the phosphate froth C. The lower angled portion 132 is angled(side view FIG. 4) and curved (FIG. 5) toward the outlet 128 to allowthe collected phosphate froth C to run therealong via gravity, as in theprior art launder 44 described above. The pipe 128 extends from thesidewall 126 near the bottom 122 of the launder 120 to allow removal ofthe phosphate froth C from the launder.

FIG. 6 shows the primary cell 62, which is exemplary of the structure ofthe cell 64, as noted above. The cell 62 generally includes the column100, the launder 120, the feed well 140, plates 150, support pipes 154,and baffles 160, 170, and 188. Each of these components will now bedescribed in greater detail.

The column 100 receives the launder 120 towards the top 106 of thecolumn 100 and is preferably welded to the launder 120. The top 106 ofthe column 100 is lower than the top 124 of the launder 120 (see FIGS. 2and 6). Due to this difference in height, the phosphate froth C can runover the top 106 of the sidewall 104 of the column 100 and into thelaunder 120, i.e., into the trough 138 formed between the column 100 andthe launder 120, where the phosphate froth C moves by gravity to thebottom 122 of the launder 120, to be removed via the outlet 128.

The angling of the launder bottom 122 (see FIG. 4) aids in the movementof the phosphate froth C by gravity. That is, the phosphate froth isrelatively tacky due to its hydrophobicity, which causes water to be“shed” from the phosphate froth frustrating any natural flow of thematerial. The sloped bottom of the launder 120 substantially eliminatesthis problem and allows for the collection of the phosphate froth nearthe pipe 128.

The feed well 140 receives the incoming slurry A via feed tube 66. Therate of the incoming slurry is controlled by a regulating device 118such as a variable speed pump, a conveyor belt or a pinch valve. Thefeed well 140 of the present invention discharges over the top 146. Inaddition, the feed well 140 of the present invention is at an adjustableheight below the operating water line 148. (See FIG. 8).

The feed well 140, having a bottom wall 142, a sidewall 144, and an opentop 146 is disposed towards the center of the column 100. The feed well140 is secured by using four equally radially-spaced plates 150 thereonwith holes to allow bolts 152 to attach to the support pipes 154. Theplates 150 allow the placement of the feed well 140 at an adjustableheight within the column 100 with respect to the support pipes 154.

Down pipes 90 are introduced into the column 100 and the feed well 140for the purpose of introducing aerated water into the cells 62 and 64and the feed well 140. (See FIGS. 2, 6 and 8). These down pipes 90 enterthe column 100 and the feed well 140 from the top and extend about 2-3pipe diameters or approximately 3 inches from the bottom 102 of thecolumn 100 and the bottom 142 of the feed well 140, respectively.

According to a preferred embodiment of the present invention, five downpipes 90 are introduced directly into the column 100. The down pipes 90are fixedly attached by clamping (not shown) to the baffles 160 of thecolumn 100. Extension rods 162 extend from the bottom of the down pipes90 attaching to horizontally disposed metal discs 190 that rest on topof a wear plate 158. The wear plate 158 rests on the bottom 102 of thecolumn 100.

Down pipes 90, e.g., two, can also be introduced directly into the feedwell 140. These down pipes 90 are clamped (not shown) to the sides 144of the feed well 140 and rest on a wear plate 159 at the bottom 142 ofthe feed well 140, in a similar manner as described above. See FIG. 8.

The wear plates 158 and 159 at the bottom 102 of the column 100 and atthe bottom 142 of the feed well 140, respectively, protect the bottoms102 and 142 from excessive wear. For example, without the plate 158, thebottom 102 of the column 100 would have to be replaced or consistentlymaintained due to excessive abrasion caused by large quantities of sandand other abrasive impurities from the slurry moving across the bottom102 of the column 100.

The wear plates 158 and 159 may be made of any material such asreinforced steel. Cladded wear plates may also be used as they providethe abrasion resistance that approaches ceramics. The wear plates 158and 159, therefore, serve the function of both support (of the downpipes 90) and protection of the bottoms 102 and 142.

It is preferred that the down pipes 90 be fixedly attached, e.g.,clamped, to the baffles 160 in the column 100 in order to ensure evendispersion of the incoming aerated water throughout the entire column100 and the feed well 140 via the down pipes 90, by substantiallyreducing any movement of the down pipes 90 due to turbulence.

The down pipes 90 are also spaced such that maximum distribution ofaerated water is allowed in the feed well 140 and the column 100.Generally, maximum distribution of aerated water may be achieved by theequidistant spatial placement of all down pipes 90 in the column 100 andthe feed well 140.

The feed well baffle 188 aids in the separation of impurities such assand from the phosphate which spills out of the feed well 140 into thecolumn 100. The feed well baffle 188 is attached to the feed well 140such that as the impurities B spill out of the feed well 140, B movesacross the feed well baffle 188 before spilling into the column 100. Thefeed well baffle 188 redirects the flow and constricts the flow areareducing turbulence in column 100. This constricting enhancescoalescence of the un-separated phosphate in B and acts to separate anysuspended impurities flowing with the rising air bubbles. The separatedimpurities fall downwardly and settle at the bottom 102 of the column100.

As shown in FIG. 7, four equally radially-spaced braces 182 extendbetween a pipe support 180 (for receiving the feed tube 66) and thefirst baffle 160, four equally radially-spaced braces 184 extend betweenthe first baffle 160 and the second baffle 170, and four equallyradially-spaced braces 186 extend between the second baffle 170 and thetop 106 of the sidewall 104 of the column 100.

With particular reference to FIG. 7 there is seen, from the inside tothe outside, the following components: the pipe support 180, the feedwell 140, the feed well baffle 188, the first baffle 160, the secondbaffle 170, the top 106 of the sidewall 104 of the column 100 andfinally the top 124 of the sidewall 126 of the launder 120.

Baffles 160 and 170 aid in the further reduction of turbulence in column100 and separation of impurities B from the phosphate C. C then spillsout of the top 106 of the column 100 into the launder 120 forcollection. It is possible to have one or more baffles depending on thedimensions of the column.

In order to maintain the column 100 level, a level control 164 is used.A level control 164 ensures that the phosphate froth C spilling into thelaunder 120 spills out evenly, reducing the spilling of any of the othercontents of the column 100 into the launder 120. The level control 164may be any conventional level control device and may be clamped to thetop 106 of the column 100. (See FIGS. 5 and 6).

A computerized process controller or programmable logic controller, e.g.an Allen Bradley model AB Micrologic 1000 PLC control interface 200,herein referred to as “PLC”, is used for a density control process 210,described below. (See FIGS. 6 and 9). The PLC 200 is coupled to a bubbletube 130, the pinch valve 94 and the regulating device 118.

FIG. 8 is a side cross-sectional view of the feed well 140. Two downpipes 90 are introduced directly into the feed well 140. See also FIGS.2 and 6. The down pipes 90 extending into the feed well may be ofsmaller diameter compared to the down pipes 90 introduced directly intothe column 100.

The shape of the feed well 140 is shown to be generally columnar. (SeeFIGS. 2, 6, and 8). However, in alternate embodiments, the feed well 140may be cubical, or conical as in U.S. Pat. No. 4,735,709, or of anothershape. The shape of the feed well 140 does not have a significant impacton the separation process so long as the down pipes 90 entering the feedwell allow for sufficient aeration of the incoming slurry.

In regard to operation of the separation system 60, reference is madeparticularly to FIGS. 2, 6, and 8. Slurry A is fed from the slurrysource 68 into the feed well 140. The incoming slurry A containspremixed collector such as tall oil, as discussed above.

The down pipes 90 introduce aerated water into the feed well 140aerating the feed slurry A. The column 100 is filled with aerated watervia the down pipes 90. Feed slurry A filling the feed well 140 andbegins frothing as the air bubbles released from the aerated water movefrom the bottom 142 of the feed well 140 in an upward flow to the top146 of the feed well 140. The aeration of A produces phosphate froth C.This upward flow of the air bubbles provides the air holdup. The airholdup carries the attached hydrophobic phosphate particles C to the top146 of the feed well 140 and to the top 106 of the column 100.

The impurities B including sand spill out from the feed well 140 overthe feed well baffle 188 and baffles 160 and 170. As discussed above,the feed well baffle 188 functions to substantially reduce theturbulence from the impurities and un-separated phosphate flowingoutward from the feed well 140 to yield substantially impurity-freephosphate froth C. Substantially most of the separation of the phosphatefrom the impurities such as sand and clay occurs in the feed well 140.

The remainder of the separation is completed inside the column 100,which also receives down pipes 90 that introduce aerated water at thebottom 102 of the column 100. C spills out of the top 106 of the column100 due to the air holdup mentioned above to be received by the trough138 formed between the column and the launder 120, where C moves bygravity to the bottom 122 of the launder 120, to be removed, whendesired, via the outlet 128 of the launder 120 of the primary cell 62.It is possible to use additional baffles towards the top of the columnto further aid in removing any remaining impurities from C. Theimpurities separated from the phosphate froth C collect at the bottom102 of the column 100 to form a sand bed “W” containing clay and otherseparated impurities as well. (See FIG. 6). The bottom of sand bed W isa plug or choked condition which can be controlled by varying the numberand the spacing of the down pipes 90 in the column 100. The number ofdown pipes 90 that may be placed within the column 100 is directlyrelated to the average particle size of the settling impurities formingthe sand bed W at the bottom 102 of the column 100.

The down pipes 90 provide the air holdup mentioned above along with evendispersion of air throughout the column 100 and the feed well 140. Thedown pipes 90 can accomplish these important functions without choking.This is possible because aerated water is thrust down the down pipes 90.The aerated water discharges at the bottom 102 of the column 100 insidethe sand bed W or at the bottom 142 of the feed well 140.

The aerated water releases the air bubbles within the sand bed W. Thesand bed W breaks up the air bubbles into a multitude of small airbubbles that rise through the sand bed substantially uniformly. The sandbed W also slows down the turbulence caused by the aerated water beingreleased via the down pipes 90 at the bottom 102 of the column 100. Asthe aerated water is introduced into the bottom 102 of the column 100via the down pipes 90, the air bubbles naturally pass through the sandbed by taking the path of least resistance. No constriction plate isused or required, unlike the prior art discussed above. Since, there isno such plate with orifices used in the present invention, there is nochoking.

It is possible for the down pipes 90 to choke, however, this problem canbe avoided by maintaining a high pressure of aerated water being thrustinto the down pipes 90 by adjusting the position of the eductors 92 withrespect to the bottom 102 of the column 100 (See FIG. 6). Aerated waterexiting at high pressure from the bottom of the down pipes 90 willprevent any possibilities of choking of the down pipes 90 because of thepressure differential created at the bottom of the down pipes 90 wherethe aerated water is released. Therefore, the incoming aerated water viathe down pipes 90 has to have sufficient air pressure in order toovercome the weight of the sand bed W.

The air bubbles being released at the bottom of a column of water, as inthe prior art (FIG. 1), achieve maximum rise velocity within 2-3 feet.As the air bubbles move towards the top of a water column formed insidethe column 100, they get larger and larger because the pressure insidethe column decreases towards the top 106 of the column 100. Thisexpansion and rise velocity creates some turbulence or a slight backeddy, which is a low-pressure zone behind these rising air bubbles. Theimpurities B, including fine particles of sand within the column,actually ‘tail gate’ this low-pressure zone behind the air bubbles. Theresult, therefore, is that it is possible to obtain a cleaner phosphatefroth C at the top of the column 106 by hindering the rise of the airbubbles.

As the separation process moves forward, it is possible to have fivevirtual zones, shown in FIG. 6, within the column 100, based on the typeof materials found in each zone separated by physical and chemicalproperties.

Zone “R” is found towards the bottom of the column and is the zonecontaining settling impurities B such as sand and clay forming the sandbed W. Zone “R” is the zone where aerated water from the down pipes 90enters the bottom 102 of the column 100. Since, the sand bed acts as adispersion plate by breaking up the air bubbles being released from theaerated water into smaller air bubbles, and also evenly dispersing theair bubbles throughout the column 100, it is important to have asubstantial quantity of sand in Zone “R” to ensure the even dispersionof the air bubbles throughout the column 100.

The next zone is Zone “S”, which is located above Zone “R”. Zone “S” isa substantially homogeneous slurry zone. Zone “S” contains a higherpercentage of un-separated phosphate particles. There is sufficientstability to allow for density measurements within Zone “S”, asdiscussed below.

The next zone is Zone “T”, which is located above Zone “S”. Zone “T” isthe contact zone, where the rising air bubbles within the column 100interact with B spilled over from the top 146 of the feed well 140. Zone“T” is generally located above the top 146 of the feed well 140. Zone“T” generally is a higher density zone compared to zones “U” and “V”,discussed below. Zone “T” contains lighter components of impurities Bsuch as clay particles, sticks, etc. that were separated from theincoming feed slurry A. The bottom of Zone “T” is where the air bubblesexit the sand bed W. The air bubbles rise rapidly in this zone but arehindered in their upward movement through the column because of thesettling sand from the top 106 of the column 100. This hindrance is moreprominent towards the bottom Zone “T” where the air bubbles are firstbeing released. The middle through the top of Zone “T” is thereforefairly turbulent. However, this provides a good environment to increasethe contact probability of any un-separated hydrophobic phosphateparticles to an air bubble to rise upward to become part of thephosphate froth C.

Zone “U” is located above Zone “T” and is the next zone moving towardsthe top 106 of the column 100. Zone “U” primarily contains clear water,rising air bubbles, and some phosphate froth rising upwards by the helpof the air holdup discussed above.

Finally, there is Zone “V”, which is located above Zone “U” and is foundon the very top 106 of the column 100. Zone “V” primarily containsphosphate froth C substantially free from impurities, spilling out thetop 106 of the column 100 into the launder 120.

As the slurry A continues pouring into the feed well 140 via feed tube66, the environment within the cell 62 keeps changing depending on thequantity and quality of the feed slurry A being introduced. Over aperiod of time, the cell 62 may tend to have one or a combination of thefollowing problems due to the fluctuations in the feed slurry A: toomuch sand is deposited in the sand bed, too much or too little slurryfeed A enters the cell 62, the particle size of the impurities includingsand is too small increasing the total surface area of the impuritieswithin the column 100 requiring more water for effective separation,etc. If one or a combination of these problems occur, the separationprocess will have to be suspended until the contents within the cell canreach equilibrium to continue with effective separation of the phosphatefroth from the impurities.

In order to avoid down time and to avoid the suspension of theseparation process, the density control process 210 can be used, asshown in FIG. 9. The PLC 200 is coupled to the pinch valve 94 andregulating device 118. The PLC 200 is also coupled to the bubble tube130 to measure the density of the contents within the column 100. Anysuitable density measuring device may be used instead of the bubble tube130.

In a preferred embodiment, as shown in FIG. 9, the density controlprocess 210 entails measuring the density of the contents within thecolumn towards the top of Zone “S” for the reasons described above byusing the bubble tube 130. One or multiple density measurements may betaken so long as the density is measured in a zone or zones where stablemeasurements can be taken, e.g., the bottom or middle of Zone “S”.

The PLC 200 reads the density measurement by the bubble tube 130 andcompares it to a stored manually adjustable set point 202 inputted intothe PLC. Then based on the comparison between the density measurementand the set point 202, the PLC 200 controls the opening or closing ofthe pinch valve 94 and the regulating device 118. The pinch valve 94controls the flow of the impurities exiting the cell 62 via outlet 108.The regulating device 118 controls the flow of the incoming slurry viafeed tube 66 within the cell 62. The density control process 210 repeatscontinuously maintaining the density within the cell 62 at the set point202.

For example, when the slurry feed A comes into the cell 62, the densityof the cell 62 automatically starts to increase. If the PLC 200 detectsthat the measured density is greater than the set point 202, the PLC 200controls the opening of the pinch valve 94 allowing the discharge of theimpurities including the sand from the bottom 102 of the column 100. ThePLC 200 also controls the regulating device 118 to suspend the entry ofthe incoming slurry feed A. The PLC 200 thus controls the opening andclosing of the pinch valve 94 and the regulating device 118 to lower thedensity within the cell 62 to the set point 202.

Similarly, if the PLC 200 detects that the density inside the cell 62has fallen below the set point 202, the PLC 200 controls the regulatingdevice 118 to allow entry of the incoming slurry feed A. The PLC 200will also control the closing of the pinch valve 94 to suspend thedischarge of the impurities from the bottom 102 of the column 100,allowing the density of the cell 62 to increase to the set point 202.The set point may be adjusted depending on temperature, pressure, typeof slurry feed being introduced, etc., by manually adjusting the setpoint 202 in the PLC 200. The density control process 210 thereforetakes into account the overall environment of the cell 62.

The cell 62 is no longer dependent on the manual control of the incomingfeed via feed tube 66 based on visual monitoring of the changes withinthe cell 62. In fact, the density control process 210 by the PLC 200reacts to changes within the cell 62 and keeps the recovery rate ofphosphate substantially stable. In a preferred embodiment of the presentinvention, the set point 202 can be preset in the PLC 200 in the rangeof about 1-1.5 specific gravity of the contents within the cell 62 ascompared to the specific gravity of water.

Although it is preferred to measure density towards the top of the Zone“S” as discussed above, it is possible to measure density at variouslocations within the column 100 so long as stable measurements can bemade. For example, another measurement of density could be taken towardsto top of Zone “U” for obtaining a differential density measurement.

The advantages of the density control process include but are notlimited to maintaining equilibrium within the cell 62, allowing acontinuous separation process, eliminating the need for regularmaintenance of the cell 62, and, most importantly, increasing phosphaterecovery and efficiency by minimizing fluctuations within the cell 62caused by the type of incoming slurry feed A, temperature, pressure etc.

As an alternative, the same process control can be achieved by measuringa pressure differential in any two stable zone. Based on the comparisonbetween pressure differential and the set point pressure differential,the pinch valve 94 and regulating device 118 can be controlled in thesame manner, and achieve the same advantages, as described above.

As can be seen from above, the present invention provides an apparatusand a process for recovering phosphate using a column flotation cellthat substantially reduces the requirement for regular maintenance ofthe cell 62 because of the use of down pipes that do not choke and thedensity control process described above.

The invention also prevents substantial choking of constriction platesbecause no such plates are required for the dispersion of air throughoutthe column. The down pipes 90 do not choke due to sufficientlypressurized aerated water that thrusts out of the bottom of the downpipes 90. Further, the sand bed in Zone “R” eliminates the need for aconstriction plate to disperse air.

This invention also allows agitation of feed and water in the bottom ofthe column which promotes better dispersion of air into the cell thanthe prior art apparatus because the sand bed in Zone “R” naturallybreaks down air bubbles into a multitude of smaller air bubbles, whileat the same time dispersing the air bubbles evenly as they rise towardsthe top of the column.

Because the invention utilizes cell density control or pressuredifferential control there is improved recovery of the phosphate.

Further, this columnar floatation cell is characterized by asubstantially compact design, relative to the prior art, which reducescapital cost for installation and reduces maintenance costs: smallercolumns are easier and cheaper to install and are easier to operate andmaintain.

Although the above description provides an example of recoveringphosphate from impurities, other minerals may be separated fromimpurities using the same apparatus and method as described above.

The many features and advantages of the invention are apparent from thedetailed specification and, thus, it is intended by the appended claimsto cover all such features and advantages of the invention that fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and changes will readily occur to those skilledin the art, it is not desired to limit the invention to the exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope of the invention.

1. An apparatus for separating a mineral from a slurry including themineral and impurities, comprising: a vessel for containing fluid andhaving a first, open end and a second end; a feed well disposed near thefirst end of the vessel, wherein the feed well has a first, open end anda second end, and wherein the first end of the feed well receives theslurry; at least one first member received through the first end of thefeed well for providing aerated water to the second end of the feedwell, releasing air bubbles that move from the second end of the feedwell toward the first end of the feed well, creating a froth in the feedwell including substantially the mineral, wherein the mineral frothsubstantially separates from the impurities and floats out of the firstend of the feed well and towards the first end of the vessel; and acollection unit having a first open end and a second end, and beinglocated at the first end of the vessel, wherein the mineral froth movesinto the first end of the collection unit from the first end of thevessel, and wherein the impurities and any remaining mineral fall bygravity towards the second end of the vessel.
 2. The apparatus of claim1, further comprising at least one measurement unit placed within thevessel for measuring at least one of density and pressure of the fluidin the vessel.
 3. The apparatus of claim 1, further comprising at leastone second member received through the first end of the vessel andproviding aerated water to the second end of the vessel, releasing airbubbles that move from the second end of the vessel toward the first endof the vessel, further creating the mineral froth.
 4. The apparatus ofclaim 1, wherein the vessel is first and second vessels, each having afirst, open end, a second end and a collection unit, wherein a fluidconduit connects the second end of the first vessel with the first endof the second vessel to transfer fluid from the first vessel to thesecond vessel, and the second vessel includes an outlet at the secondend for removing impurities, and each collection unit includes an outletfor recovering the mineral froth.
 5. The apparatus of claim 1, whereinthe feed well is adjustably mounted relative to the vessel.
 6. Theapparatus of claim 1, wherein the slurry comprises a collector and afrother.
 7. The apparatus of claim 6, wherein the frother ishydrocarbon.
 8. The apparatus of claim 1, wherein the at least one firstmember is a pipe disposed a distance of about 2-3 diameters of the pipefrom the second end of the feed well.
 9. The apparatus of claim 3,wherein the at least one second member is a pipe disposed a distance ofabout 2-3 diameters of the pipe from the second end of the vessel. 10.The apparatus of claim 1, wherein the at least one first member is twospaced pipes.
 11. The apparatus of claim 3, wherein the at least onesecond member is five equally-radially spaced pipes.
 12. The apparatusof claim 1, wherein at least one baffle is positioned at the first endof the vessel to further separate the mineral froth from the impurities.13. The apparatus of claim 1, wherein at least one baffle is positionedat the first end of the feed well to further separate the mineral frothfrom the impurities.
 14. The apparatus of claim 1, wherein the at leastone first member provides the aerated water at high pressure.
 15. Theapparatus of claim 3, wherein the at least one second member providesthe aerated water at high pressure.
 16. The apparatus of claim 2,wherein a plurality of zones is formed within the vessel based ondifferences in at least one of density and pressure of the fluid,including a relatively most dense/highest pressure zone at the secondend of the vessel and a relatively least dense/lower pressure zone atthe first end of the vessel, and wherein the measurement unit provides ameasurement of said at least one of density and pressure in the fluidbetween the first and second ends of the vessel.
 17. The apparatus ofclaim 16, wherein when the measurement is greater than a predeterminedamount, less slurry is added to the feed well.
 18. The apparatus ofclaim 16, wherein when the measurement is less than a predeterminedamount, more slurry is added to the feed well.
 19. The apparatus ofclaim 17, wherein the predetermined amount is in the range of about1-1.5 specific gravity.
 20. The apparatus of claim 1, wherein the vesselhas a width of about 10 feet.
 21. The apparatus of claim 1, wherein thevessel has a height of about 6 feet.
 22. The apparatus of claim 1,wherein the vessel has a height and a width, and a ratio of the heightto the width is in the range of about 0.5-2.
 23. The apparatus of claim22, wherein the ratio in the range of about 0.6-1.33.
 24. The apparatusof claim 2, wherein the at least one measurement unit is a bubble tube.25. The apparatus of claim 1, wherein the at least one first member isfixedly connected relative to the feed well.
 26. The apparatus of claim3, wherein the at least one second member is fixedly connected relativeto the vessel.